Carbon nanotubes (CNTs) have been proposed for use in a number of applications that can take advantage of their unique combination of chemical, mechanical, electrical, and thermal properties. Various difficulties have been widely recognized in many applications when working with individual carbon nanotubes. These difficulties can include the propensity for individual carbon nanotubes to group into bundles or ropes, as known in the art. Although there are various techniques available for de-bundling carbon nanotubes into well-separated, individual members (e.g., including sonication in the presence of a surfactant), many of these techniques can detrimentally impact the desirable property enhancements that pristine carbon nanotubes are able to provide. In addition to the foregoing, widespread concerns have been raised regarding the environmental health and safety profile of individual carbon nanotubes due to their small size. Furthermore, the cost of producing individual carbon nanotubes may be prohibitive for the commercial viability of these entities in many instances.
Polymer composites formed from carbon nanotubes are often electrically conductive and strongly absorb microwave radiation, particularly at carbon nanotube concentrations above the percolation threshold. However, the propensity of individual carbon nanotubes to agglomerate with one another in ropes or bundles can make the formation of polymer composites containing well separated carbon nanotubes problematic. Carbon nanotube agglomeration of this type does not generally allow the beneficial properties of the carbon nanotubes to be expressed to the same degree and conveyed to the polymer matrix as well as when individual carbon nanotubes are present.
Microwave transmission assemblies are configured to convey microwave radiation along the interior of the assembly through reflection at the assembly walls, with minimal absorption and scattering. Microwave transmission assemblies can include both simple waveguides and coaxial cable, but they can also include more complex structures such as flexible waveguides, waveguide rotary joints, waveguide switches, and even more complex assemblies. To effectively convey microwave radiation along the interior of the assembly, the internal reflecting surfaces need to be electrically conductive and meet rigorous manufacturing standards that reduce the incidence of microwave scattering. Metals have most often been used for this purpose, most typically copper and bronze, since they are electrically conductive and can be easily machined in most cases. The metal can be chosen to regulate the frequency of microwave radiation that is transmitted. However, some metals can be expensive to source and machine, and particularly in the case of waveguides, they can add an excessive amount of unwanted weight, which can be detrimental in aeronautic and aerospace applications, for example. Moreover, rigorous quality control specifications and machining tolerances can considerably add to the cost of producing microwave transmission assemblies fabricated from metals. Although carbon nanotubes have been considered as a replacement for metals in some applications, the aforementioned difficulties of working with carbon nanotubes has not yet allowed these entities to be used as an adequate replacement for metals, particularly in microwave applications. Moreover, the strong absorption of microwave radiation by carbon nanotubes has generally precluded their consideration for microwave transmission applications.
In view of the foregoing, production of carbon nanotubes in a form that renders them more amenable for use in various microwave power applications would be highly desirable. The present disclosure satisfies the foregoing needs and provides related advantages as well.